Plasma etch chambers for processing semiconductor substrates are well known and can be exemplified by reference to the prior art chamber of FIG. 1.
Referring to FIG. 1, a semiconductor substrate to be etched 20 is mounted on an RF powered cathode support pedestal 22 which is mounted in a vacuum chamber 10. A showerhead gas distribution plate 26 allows etchant plasma precursor gas to enter the vacuum chamber from an external source 28. The gas distribution plate 26 can also act as the anode which is electrically grounded. A source of coolant gas can also be supplied to the chamber through a passage 32 in the pedestal 22. The coolant gas enters the space between the backside of the substrate 20 and the top of the support pedestal 34 and serves to couple the temperature regulated support pedestal 22 and the substrate 20 to ensure temperature regulation of the substrate 20 during processing. The support pedestal 22 can be heated or cooled during processing; however, generally the large thermal mass of the support pedestal 22 relative to the mass of the substrate 20 serves to dissipate heat generated in the substrate 20 during the plasma etching process, thereby controlling the substrate temperature during processing.
Surrounding the pedestal support 22 is a cylindrical support 36 which is larger in diameter than the pedestal support 22, to allow independent vertical movement of the cylindrical support 36.
In addition, a metal clamping ring 38 overlies the substrate 20 during processing. The clamping ring is supported on the cylindrical support 36 at all times. During processing, the cylindrical support 36 is lowered so that the clamping ring 38 contacts the substrate 20.
Since the prior art etch chamber of FIG. 1 is meant for continuous operation, particulates can build up in the chamber from various plasma and etch species. Since if these particulates deposit onto the surface of the substrate 20 they will reduce the yield of good devices from the substrate 20, reduction of particles generated in the etch chamber and prompt removal of any particulates that do form during processing is mandatory.
Thus a continuous load lock purge has been used to maintain a positive pressure between an adjacent load lock chamber and the processing etch chamber, and to prevent particulates from contact with the substrate. This continuous load lock purge has been moderately successful in reducing the formation of particles and in the prompt removal of any particles that do form in the chamber.
The chamber 10 is designed for continuous usage and many hundreds of substrates are desirably processed consecutively before taking the chamber 10 apart for cleaning. Thus the chamber 10 become more contaminated and the number of particles therein increases over time. Since cleaning the chamber 10 is expensive, we sought to determine the causes of particle generation in the above chamber and to find ways of reducing the number of particles generated and collected in the chamber, both to reduce contamination of the substrates and to increase the time or number of processing cycles between cleanings.